Nuclear fuel rods often are produced from alloys of zirconium metal. Zirconium provides a combination of high corrosion resistance, high strength at moderate and high temperatures, and a low neutron-absorption cross section which makes the metal ideal as a fuel rod cladding material.
However, slight impurities in zirconium adversely affect the mechanical properties of the metal, especially at higher temperatures such as the operating temperature of a nuclear fuel reactor. As a result, special zirconium alloys, such as zircaloy and zirlo, have been developed for greatly improving the oxidation resistance of the fuel rod at higher temperatures. As a result, nuclear fuel manufacturers are providing nuclear fuel rods made of zirlo and zircaloy cladding to resist corrosion and degradation at higher temperatures.
In some nuclear reactor cores, zirlo alloy fuel rods are more preferred because the special alloy materials found in the zirlo makes that material more corrosion resistant than zircaloy. It has been determined that zircaloy rods may fail if they inadvertently are inserted in a reactor core designed for use with zirlo rods. This may cause a reactor to shut down resulting in increased costs and maintenance.
In some nuclear fuel manufacturing plants, zircaloy and zirlo fuel rods are processed concurrently with each other. It is possible during the manufacturing process for one type of rod, such as a zircaloy rod, to become mixed into a group of zirlo rods. Because both zirlo and zircaloy rods are similar in appearance, weight, dimension and handling characteristics, it is almost impossible to segregate the zirlo and zircaloy fuel rods without appropriate inspection procedures. It is necessary, therefore, to segregate zirlo and zircaloy fuel rods during processing.
Additionally, any inspection and segregation process for the rods must be nondestructive to the rods. Manufacturing nuclear fuel rods is an expensive process and any destructive alloy verification and segregation system is unacceptable and costly. Statistical random selection of fuel rods for alloy verification and segregation also is unacceptable because statistical inspection procedures cannot give one hundred percent verification of each processed fuel rod. Additionally, any inspection and segregation process should be automated with appropriate rod and material handling systems to accommodate peak production requirements and facilitate the segregation of different fuel rods.
It has been determined that a thermoelectric testing system, commonly referred to as a Seebeck effect testing system, is more desirable than other non-destructive testing methods such as x-ray fluorescence which requires expensive equipment, or eddy current testing which requires a separate test coil. An eddy current testing system is considered impractical in a nuclear fuel rod production environment because different rods of varying diameters often are processed together. The eddy current test coil is sized depending on the dimensions of a rod or other material to be tested. Thus, an eddy current testing apparatus may not only require a number of different sized test coils, but also the means for measuring the rods and transferring the rods to the appropriate coil.